Preparation of electrical and refrigerator oils



United States Patent 3,145,161 PREFPARATEUN (3F ELECTRTCAL ANDREEEELQEERATUR @iilLS Frank E. Anderson, Springfield, and ivor W. Mills,Glenolden, Pan, assignors to Sun Company, Philadelphia, li es, acorporation of New Jersey No Drawing. Filed Nov. 26, 11962, Ser. No.244L146 12 (Claims. (Ci. ass-e75 This invention relates to thepreparation of electrical oils and refrigerator oils having a highoxidation resistance and a high degree of inertness to Freon typerefrigerants.

In the use of electrical oils such as transformer oils, cable oils, andthe like it is important that the oil have a high resistance tooxidation in order to avoid the formation and accumulation ofsludge-like deposits Within the equipment. In addition, in arefrigeration system using a Freon type refrigerant such as Freon-12(dichlorodifluoromethane) it is important that the refrigerator oil beinert to the refrigerant because any reaction between the oil andrefrigerant produces highly corrosive hydrochloric acid. Consequently, amethod of preparing electrical oils of high oxidation stability andrefrigerator oils of a high degere of inertness to Freon typerefrigerants is highly desirable.

A commonly used test for determining the oxidation stability ofelectrical oils is known as the Doble Oxidation Test. This procedure hasbeen described in ASTM Standards on Electrical Insulating Liquids andGases,

pages 307-313, December 1959, under the title Suggested Method of Testfor Oxidation Characteristics of Mineral Transformer Oil. It involvesbubbling air through a known amount of the oil held at a temperature of95 C. in the presence of copper and iron and making two types of testsdaily on small samples of the oil. One type of test is an aciditymeasurement. The other is a precipitation test in which one volume ofthe oil is diluted with five volumes of pentane, the mixture is allowedto stand at least eight hours and the presence or absence of a sludgeprecipitate is noted. The end point of the Doble test is taken as thenumber of days of oxidation either before the acidity of the oil reaches0.25 mg. of KOH per gram or before a positive precipitation test forsludge is obtained.

A procedure used to obtain a measure of the inertness of refrigeratoroils to Freon type refrigerants is known as the Continental OxidationTest. This procedure is described at pages 314-317 in ASTM Standr r ardson Electrical Insulating Liquids and Gases, Decemoer 1959. Results ofthis test are expressed in terms of hours before a given amount ofoxygen absorption has occurred under certain oxidation conditions. Itshould be noted that while the oxidation stability per se ofrefrigerator oils is not overly important, since such oils are usuallyused in closed systems which contain no oxygen, the oxidation stabilityof refrigerator oils has been traditionally regarded by commercial usersof such oils as a measure of the inertness of such oils to Freon typerefrigerants. Oils having improved oxidation stability havetraditionally been found to have improved inertness to Freon typerefrigerants.

Another procedure used to determine the reactivity of refrigerator oilswith Freon type refrigerants is known as the Sealed Tube Test and isdescribed in Refrigerating Engineering, July 1952, at pages 737-742. Theprocedure involves placing equal volumes of the oil and refrigerant,usually Freon-l2, and a small strip each of copper and iron in a glasstube which is then evacuated, sealed, and held at 347 F. As the oil andrefrigerant react, the mixture becomes progressively darker. The

ddidddihi end point of the test is taken as the number of days beforethe mixture becomes black.

A conventional procedure for refining oils to make electrical orrefrigerator oils involves a preliminary solvent extraction such asextraction with furfural, treatment of the resulting raffinate withconcentrated sulfuric acid typically in amount of 5-30 lbs./bbl. andthen treatment with adsorptive clay typically in amount of 20-40lbs./bbl. This procedure, however, often does not produce an oil havingsatisfactory oxidation resistance or satisfactory inertness to Freontype refrigerants. Hence a more effective treatment is needed.

A method has now been found by which electrical oils of outstandingoxidation stability and refrigerator oils of outstanding inertness toFreon type refrigerants can be prepared. The method comprises the stepsof (1) treating the charge oil with concentrated sulfuric acid, (2)neutralizing the acid treated oil, (3) contacting the neutralized oilwith copper, and (4) treating the acid treated, neutralized, coppercontacted oil with adsorptive clay.

Before describing the invention in detail it is desirable to brieflydiscuss known methods of treating mineral oils. The literature andpatent art abound with suggested methods for treating petroleumfractions with copper. These methods are generally directed to theremoval of sulfur compounds from petroleum fractions, and the methodsarose many years ago when sulfur compounds were first recognized asgenerally undesirable constituents of most petroleum fractions. However,when these known methods are applied to the preparation of refrigeratoroils and electrical oils such as transformer oils, there is little ifany improvement in the oil, either with respect to sulfur content orwith respect to oxidation resistance and inertness to Freon typerefrigerants. The lack of improvement in sulfur content is due to thefact that electrical and refrigerator oil charge stocks have invariablyalready been treated with sulfuric acid and hence contain eitheressentially no sulfur or an amount of sulfur which is so small that nofurther reduction is effected by the known copper treating procedures.The reason why known copper treating procedures fail to effect anyimprovement in either the oxidation resistance of electrical oils or theinertness of refrigerator oils to Freon type refrigerants is that theknown procedures do not contain the precise conditions necessary toeffect such improvement.

According to the present invention, electrical oils of outstandingresistance to oxidation and refrigerator oils of outstanding inertnessto Freon type refrigerants are obtained by a treating procedure whichcomprises:

(1) Treating the charge oil with 5-30 lbs. per barrel of concentratedsulfuric acid.

(2) Neutralizing the acid treated charge oil.

(3) Contacting the acid treated, neutralized charge oil in liquid phasewith 0.3-5 .0%, preferably (Hi-3.0% metallic, i.e., elemental, copper ata temperature of -5O0 E, preferably -350 E, the copper being depositedon an inert support and the contacting being by the contact technique asopposed to the percolation technique.

(4) Treating the sulfuric acid treated, neutralized, cop per contactedcharge oil with 1-40 lbs. per barrel of adsorptive clay.

The charge oils of the invention are conventional electrical andrefrigerator oil charge stocks. They are mineral distillate oils,usually naphthenic distillate oils obtained from Coastal crudes, andthey have viscosity-gravity constants in the range of 0.84 to 6.92.which corresponds to aromatic contents generally in the range of 15-65%by weight. The viscosity, boiling range, and other physical propertiesof the charge oils will vary depending upon the ultimate use of thefinal oil product.

For example, a transformer oil charge stock will usually have an S.U.S.viscosity at 100 F. in the range of 50-65 while a refrigerator oilcharge stock will usually have an S.U.S. viscosity at 100 F. in therange of 100-700. However, it is characteristic of all the charge oilsof the invention that they have viscosity-gravity constants in the rangeof 0.84 to 0.92. In some cases the charge oil will have been subjectedto a preliminary extraction with a solvent such as furfural, but this isnot necessary to the operability of the invention.

As described, the charge oil is initially treated with sulfuric acid.The sulfuric acid should be concentrated, i.e., 90l00%, and should beused in the amount of 30, preferably 10, pounds of acid per barrel ofoil (1 bbl.=42 gallons). Conventional sulfuric acid treatingtemperatures of 70200 F. are satisfactory for the present purpose. Theacid treatment of the oil is conveniently carried out by adding theprescribed amount of acid to the oil in a tank equipped with anagitator. Upon adding the acid to the oil, essentialy two liquid phasesresult. One is an acid phase, the other is an oil phase. In addition,some sludge usually forms by reaction of the acid with the oil. Aftermixing for, say, 30 minutes, the agitation is stopped and the phases areallowed to separate. The acid and sludge settle to the bottom of thetank, the oil phase remains on the surface and is then separated by, forexample, decanting.

It should be noted that the amount of sulfuric acid specified above,i.e., 5-30 lbs./bbl., is a relatively light acid treatment and willeffect essentially no change in the viscosity'gravity constant of thecharge oil. in other words, the viscosity-gravity constant of the acidtreated oil is essentially the same as that of the charge oil.Similarly, the next step of the invention, i.e., neutralization, alsoresults in essentially no change in the viscosity-gravity constant ofthe charge oil.

The acid treated oil is next neutralized, i.e., the acidity which ispresent in the oil after the sulfuric acid treatment is eliminated. Evenafter the sulfuric acid phase is separated from the acid treated oil,there is some acidity present in the oil which must be neutralized ifthe subsequent treatment with copper is to be efiective. Theneutralization of the acid treated oil can be done in any convenientmanner. One method is to treat the acid treated oil with an adsorptiveclay. Any conventional adsorptivc clay such as fullers earth and thelike can be used. Generally 5-40 lbs. clay per barrel of oil will besutlicient to effect neutralization. Conventional clay treatingtemperatures of 150 to 300 F., preferably 210 to 250 F, are satisfactoryfor the present purpose. The clay treatment can be by the contact orpercolation method. Thus the clay can be added to a tank containing theacid treated oil, the mixture agitated, and the clay then separated fromthe oil by filtration. Alternatively the oil can be passed through acolumn containing the clay.

Alternatively, the acid treated oil can be neutralized by washing withan alkaline material, caustic soda (NaOl-l) being the preferred materialfor economic reasons. in most cases, neutralization of the acid-treatedoil can be effected by Washing the oil with 5%, by volume of the oil, of5 Be. NaOl-l. Excess NaOl-l can then be removed by washing the oil oneor more times with water. The result is an oil which is usually slightlybasic but such basicity is unimportant for the present purpose. Theimportant quality of the oil resulting from this neutralization step,and the meaning of neutralization as herein used, is that it has noacidity, as determined by pH, titration with KOH, or the like.

The acid treated, neutralized oil is next treated with copper. There areseveral essential conditions involved in the copper treating step andeach must be observed if the beneficial results of the invention are tobe obtained.

One essential feature is that the copper used as copper metal, i.e.,elemental copper. Copper salts, whether they be cupric or cuprous salts,have been found to be inoperable for the present purpose.

Another essential feature is that the copper is deposited on an inertsupport. Merely treating the oil with copper metal alone, in conjunctionwith the other treatments herein specified, will not give the beneficialresults of the invention. The support is described as inert because itundergoes essentially no reaction with either the oil or with the copperunder the conditions of the treatment. Examples of suitable inertsupports are silica gel, silica, montmorillonite, and other clays,pumice, bauxite, and the like. Silica gel is preferred.

The copper can be deposited on the inert support by any convenientmethod. One method is to impregnate the support with a solution of acopper salt, oxidize the copper salt to copper oxide, and then reducethe copper oxide to copper metal by heating in an atmosphere ofhydrogen. For example, the support is impregnated with copper acetateand is then heated to and held at, say 700 F. in an atmosphere of airfor, say, l0-20 hours. The resulting copper oxide is then held at, say,700 F. for, say, l5 hours in an atmosphere of hydrogen. In some cases itwill be desirable to repeat the deposition procedure in order to obtainthe desired amount of copper on the support.

The amount of copper deposited on the support can vary over wide limitsand will depend upon such factors as the surface area of the carrier,the amount of carrier which it is desired to use, and the like.Generally the amount of copper will be 1 to 300% by weight of thesupport.

in the treatment of the acid treated oil with the copper, it is anessential feature that the treatment be by the contact technique incontradistinction to the percolation technique. In petroleum refiningthese two terms,

. c.g., contact and percolation, relate to methods of treatin" a liquidwith a solid and each term has a conven tional, well-known connotation.In the percolation method of treating a liquid with a solid, the liquidis pumped or otherwise caused to flow through a bed of particles of thesolid. The solid is in a relatively fine state of division in order tomaximize the amount of solid exposed to the liquid. in this type oftreatment the solid particles remain substantially fixed in position,their only motion being that created by the inherent turbulence of theflowing liquid. An example of the percolation technique involves the useof a cylindrical column filled with particles of the solid and fitted ateach end with a screen of appropriate mesh to prevent the escape of thesolid particles from the column. The liquid to be treated is pumped intothe bottom (or the top) of the column and is allowed to how, i.e.,percolate through the bed of solid particles.

In the contact method of treating a liquid with a solid, the particlesof solid are thoroughly dispersed in the liquid by some means ofagitation which may be, for example, a motor driven paddle typeagitator, air sparging, or the like. Usually the dispersion is carriedout in a conventional mixing tank. After mixing, the solid particles areseparated from the liquid. The separation is most commonly eiiccted byfiltration although other methods can be employed in some cases. Thus,if the solid is substantially more dense than the liquid, the solid canbe separated by settling and decantaion. From the above it is apparentthat the significant difference between the contact and percolationmethod is that in the former some positive method of dispersing thesolid in the liquid is utilized.

As described hereinbefore, the beneficial results of the invention arenot obtained unless the treatment of the oil with the copper is by thecontact method as opposed to the percolation method. Although the reasontherefore is not definitely known, it has nevertheless been found thatwhen the acid treated neutralized oil is precolated through a bed ofcopper deposited on an inert carrier,

the final oil does not have outstanding resistance to oxidation andoutstanding inertness to Freon type refrigerants. The oil issubstantially inferior to an oil which has been prepared in the samemanner except that the copper treating step is by the contact method.

In order to determine the reason for this unusual result, severalpossible explanations were investigated. One explanation is that whenthe copper and acid treated oil are mechanically agitated in a tank,i.e., when the contact method is employed, oxidizing conditions areinherently present because of the surrounding atmosphere of air and thetendency of any mechanical agitation to inject surrounding air into theliquid being mixed. Conversely, oxidizing conditions would not bepresent when percolating the oil through copper in a closed column.However, this explanation is not satisfactory, for when the acid treatedoil is agitated with the copper in a tank maintained in an atmosphere ofnitrogen, the final oil still has the same outstanding properties.Hence, oxidizing conditions during the copper treating step are not theexplanation nor are they essential to the operability of the invention.

Another possible explanation is that the percolation method of treatingan oil with copper does not provide the same intimate, efficient,thorough mixing of the oil with the copper that the contact methodprovides. However, even when the rate at which the oil is percolatedthrough a bed of copper is substantially reduced, in order to increasethe residence time, there is little improvement in the oxidationresistance or inertness to Freon type refrigerants of the final oil. Forexample, when the contact method is used, a one hour residence time ofcopper in the oil is more than sufficient to provide an oil of outstanding properties. When the percolation" method is used, a residencetime as high as 4 hours results in essentially no improvement. Ifefficiency of mixing was the responsible factor, it would be expectedthat the percolation method would result in at least some significantimprovement. This has not, however, been found to be the case.

As used in the appended claims with reference to treating an oil withcopper, the term contact is limited to its specialized meaning asdefined above and as conven tionally used in the petroleum refining art.

The amount of copper that should be used in the copper treating step is03-50%, preferably 0.73.0%, based on the weight of the acid treated oiland not including the support on which the copper is carried.

The temperature at which the copper is contacted with the oil should beat least 100 F. and can be as high as 500 F. Preferably, however, thetemperature is in the range of 150 F. to 350 F. The duration of thecopper treatment will vary depending upon such factors as thetemperature selected, the degree of dispersion of the copper in the oil,and the like but will generally be of the order of minutes to 3 hours.

It is another essential feature of the copper treating step that it is aliquid phase treatment. Treating the oil in the vapor phase with copperhas been found inoperable for the present purpose. Consequently, forwhatever temperature is selected for the copper treating step sufiicient pressure should be employed to maintain the oil in the liquidphase.

The removal of the copper from the copper treated oil can be effected inany of several ways. Where it is desired to reuse the copper, it ispreferably separated by, for example, filtration prior to the claytreatment step. This is not necessary, however, for the clay treatmenstep itself will remove the copper from the oil.

The acid treated, neutralized, copper contacted oil is next treated withadsorptive clay. Any conventional ad sorptive clay such as fullers earthand the like can be used. The amount of clay used should be in the rangeof 1 to 40 lbs. of clay per barrel of oil. Conventional clay treatingtemperatures of 150 to 300 F, preferably 210 to 250 F., are satisfactoryfor the present purpose. Unlike the copper treatment, the clay treatmentcan be by the contact method or the percolation method. Thus the claycan be added to a tank containing the oil, the mixture agitated, and theclay then separated from the oil by filtration. Alternatively the oilcan be passed through a column containing the clay.

The following examples illustrate the invention more specifically.

EXAMPLE I A commercial silica gel was thoroughly mixed with a 9.6percent by weight aqueous copper acetate solution in weight ratio of 55parts solution to 44 parts gel. The wet gel was then placed in an ovenand held at about 750 F. for 16 hours while purging the oven with air.Next the gel was held at about 600 F. for 1 hour while purging the ovenwith hydrogen. At the end of this period the gel was removed andidentified as copper metal on silica gel. The gel analyzed 39 percent byweight copper metal.

EXAMPLE H The charge oil was a naphthenic distillate stock suitable forelectrical transformer use. The oil initially had the followingproperties: A.P.l. gravity=24.4; flash point :380 E; fire point=310 F;S.U.S. viscosity at F.=55.3; S.U.S. viscosity at 210 13:33.6; viscosity'gravity constant=0.88; and sulfur content=0.2 percent.

The above oil was first extracted with furfural using only enoughfurfural to yield 95 percent rafilnate. The viscosity-gravity constantof the ratfinate oil was 0.87. The raflinate oil was treated at F. with20 lbs./bbl. of 99 percent sulfuric acid. The acid-treated oil was mixedat 210 F. with 35 lbs./bbl. of fullers earth after which the clay wasseparated by filtration. The clay treated oil had a Doble life of 2 daysand was identified as Oil A. Oil A had a sulfur content of 0.1 percentand an acidity of 0 mg. KOH per gm. of oil.

EXAMPLE Ill A portion of Oil A of Example ll was charged to a tankequipped with an agitator and maintained in an atmosphere of nitrogen.Next, 1 percent, as copper, based on weight of oil, of the copper metalon silica. gel prepared in Example I was charged to the tank. Themixture was heated to and held at F. for one hour after which the copperon silica gel was separated by filtration through a millipore filterwhich had a cellulose filter medium. The filtrate oil was mixed at 210F. with 5 lbs./bbl. fullers earth, after which the clay was removed byfiltration through paper. The finished oil had a Doble life of 6 days.These results show that treating an electrical oil according to theinvention effects a substantial improvement in the oxidation stabilityof such an oil. The sui fur content of the finished oil was 0.1 percent.

EXAMPLE IV In this example the copper treating step was by thepercolation technique. The percolation column was a 17 /2-inch length ofglass pipe wrapped with heating tape. The column was positionedvertically and the bottom of the column fitted with a 60 mesh screen.Two inches of glass wool were packed on top of the screen. The next 13/2 inches of the column was packed with a known amount of the coppermetal on silica gel prepared in Example I. The final 2 inches of thecolumn was packed with glass wool. A portion of Oil A prepared inExample H was heated to 175 F. and caused to flow downwardly through thecolumn. The column temperature was maintained at 175 F. with the heatingtape. The flow rate Was adjusted so that the residence time or" the oilin the bed of copper metal on silica gel was 2 hours. The oil thatdischarged from the bottom of the column, i.e., the efiluent oil, wascollected until the amount collected was 100 times the weight of copperin the bed. The oil collected was thus treated with 1 percent copper,based on ale-5,161

7 the weight of the oil, for 2 hours. The collected oil was mixed at 210F. with lbs./bbl. of fullers-earth after which the clay was removed byfiltration through paper.

EXAMPLE V1 To another portion of Oil A obtained in Example II was added1 percent by weight, based on the oil, of finely divided copper metal.The copper was not supported on an inert carrier. The copper metal had aparticle size of 100 percent through 200 mesh Tyler Standard Screen. Theoil-copper metal mixture was held at 175 EXAMPLE VII The charge oil wasanother oil suitable for electrical transformer use. The oil initiallyhad the following properties: ARI. gravity:25.2; flash point=305; firepoint=335; S.U;S. viscosity at 100 F.=58.4; S.U.S. viscosity at 210F.:34.2; viscosity-gravity constant=0.90; sulfur content=0.12 percent.

The above charge oil, not solvent extracted, was acidtreated by the sameprocedure as in Example ii. The acid-treated oil Was neutralized byWashing with 5. percent by volume of oil, 5 es. NaCH and was then washedwith 4 volumes of water per volume of oil to remove excess NaOH. Theneutralized oil was identified as Oil of 0 mg. KOH/gm. or oil, and aDoble life of 3 days.

The finished oil had a Doble life of 7 days. content of the finished oilwas 0.05%.

EXAMPLE X Another portion of Oil B obtained in Example V II was treatedby the same procedure as in Example III except that the final claytreating step was omitted. In other words, the copper contacted oil wasfiltered through a rnillipore filter. The filtrate oil had a Doble lifeof 3 days. This result shows, in conjunction with the result of ExampleTX, the necessity of the final clay treating step.

EXAMPLE XI The charge oil was a napththenic distillate oil suitable forpreparation of refrigerator oils. The oil had the following properties:A.P.li. gravity=19.5; flash point=330 1 pour point=- E; S.U.S. viscosityat 100 F. :167; S.U.S. viscosity at 210 F.:46; viscosity-gravityconstant:0.90; sulfur content:0.3 percent.

The above charge oil was treated at 125 F. with 10 lbs/bbl. of 93%sulfuric acid. The acid treated oil was then mixed at 210 F. with 20lbs./bbl. of fullers earth after which the clay was separated byfiltration. The sulfur content and acidity of the clay treated oil were0.07% and 0 mg. KOH/gm. of oil respectively. The clay treated oil had aContinental Oxidation life of 10 hours and a Sealed Tube life (usingFreon-12 as the refrigerant) of 45 days. The clay treated oil wasidentified as Oil C.

The sulfur EXAMPLE XII A portion of Oil C obtained in Example XI wastreated by the same procedure as in Example III. The finished oil had aContinental Oxidation life of 20 hours and a Sealed Tube life (usingFreon-12 as the refrigerant) of '75 days. The sulfur content of thefinished oil was 0.07 percent. These data show that treating the oil bythe method of the invention substantially improves the inertness of theoil to Freon-type refrigerants.

The results of the Examples ll-XII above are summarized in Table 1below. In order to facilitate comparison of the results, the threedifferent charge oils used are designated as Charge Oils 1, 2, and 3.

Table I Treating Stops Results Charge Copper Example Oil Sulfuric ClayDoble Conti- Sealed Acid, Method of Treat- Lite mental Tube lbs./bbl.Neutralization Form of Method of Time ment, (Days) Life Life CopperTreatment (hrs) lbs./bbl. (Hours) (Days) It 1 20 Clay No CooperTreatment None 2 II 1 20 Copper Metal ontact 1 5 6 on Silica Gel. IV T 12O 1o Percolation.-. 2 5 3 V 1 20 d0 4 5 3 VI 1 20 Copper Metal 1 5 3(No support). VII 2 20 NaOH and Water... No Copper Treatment N one 3VIII 2 20 do No C0 per Treatment 5 3 IX 2 20 do Copper Metal Contact 1 57 on Silica Gel. 2 20 .do .do .Jlc 1 None 8 3 10 No Go per Treatment 105 3 10 Copper Metal Contact 1 20 75 on 1Silica Ge EXAMPLE Vill A portionof Gil l3 obtained in Example Vii was mixed at 210 F. with 5 lbs./bbl.of fullers earth after which the clay was separated by filtrationthrough paper. The filtrate oil had a Doble life of 3 days.

EXAMPLE TX Another portion of Oil B obtained in Example VII was treatedby the same procedure as in Example ill.

It is apparent from the data contained in Table Ithat the oxidationresistance of electrical oils and the inertness to Freon-typerefrigerants of refrigerator oils are very substantially improved bytreating such oils bythe method of the invention. It is also apparentthat deviations from the method will result in no such improvement.

We claim:

1. Method of preparing electrical and refrigerator oils comprising thesteps of (1) treating a mineral distillate oil having aviscosity-gravity constant in the range of 0.84 to 0.92 with -30 poundsof concentrated sulfuric acid per barrel of oil, said treating being ata temperature in the range of 70-200 F., (2) neutralizing theacidtreated oil, (3) contacting the acid-treated, neutralized oil inliquid phase at a temperature in the range of 100 F. to 500 F. with0.3-5.0 percent by Weight of copper metal based on the oil, said coppermetal being deposited on an inert support, and (4) treating theacid-treated, neutralized, copper contacted oil with adsorptive clay.

2. Method according to claim 1 wherein the amount of copper metal is0.7-3.0 percent.

3. Method according to claim 1 wherein said temperature in step (3) isin the range of 150350 F.

4. Method according to claim 1 wherein said support is silica gel.

5. Method according to claim 1 wherein said neutralization is bytreating the acid-treated oil with adsorptive clay.

6. Method according to claim 1 wherein said neutralization is bytreating the acid-treated oil with aqueous sodium hydroxide.

7. Method according to claim 1 wherein said adsorptive clay in step (4)is used in amount of 1-40 lbs. clay per barrel of oil.

8. Method of preparing electrical and refrigerator oils comprising thesteps of (1) admixing, with agitation and at a temperature in the rangeof 100-500 F., a mineral distillate oil which has been treated with 5-30lbs./bbl. of concentrated sulfuric acid at a temperature in the range of-200 R, which has been neutralized after said sulfuric acid treatment,and which has a viscosity-gravity constant in the range of 0.84 to 0.92with copper metal, said copper metal being deposited on an inert supportand the amount of said copper metal being 0.3-5.0 percent by weightbased on the oil, whereby a copper-treated mineral. distillate oil isobtained; (2) treating said coppertreated mineral distillate oil with1-40 lbs./bbl. adsorptive clay and (3) recovering an oil of improvedoxidation resistance.

9. Method according to claim 8 wherein the amount of copper metal is0.7-3.0 percent.

10. Method according to claim 8 wherein said admixing is at atemperature in the range of -350 F.

11. Method according to claim 8 in which the oil recovered in step (3)has approximately the same sulfur content as said mineral distillate oilprior to copper treat ment.

12. Method according to claim 8 wherein said support is silica gel.

References Cited in the file of this patent UNITED STATES PATENTS ColinNov. 5, 1901 Von Fuchs et a1 Mar. 17, 1942 OTHER REFERENCES

1. METHOD OF PREPARING ELECTIRCAL AND REFRIGERATOR OILS COMPRISING THESTEPS OF (1) TRATING A MINERAL DISTILLATE OIL HAVING A VISCOSITY-GRAVITYCONSTANT IN THE RANGE OF 0.84 TO 0.92 WITH 5-30 POUNDS OF CONCENTRATEDSULFURIC ACID PER BARREL OF OIL, SAID TREATING BEING AT A TEMPERATURE INTHE RANGE OF 70*-200*F., (2) NEUTRALIZING THE ACIDTREATED OIL, (3)CONTACTING THE ACID-TREATED, NEUTRALIZED OIL IN LIQUID PHASE AT ATEMPERATURE IN THE RANGE OF 100* F. TO 500*F. WITH 0.3-5.0 PERCENT BYWEIGHT OF COPPER METAL BASED ON THE OIL, SAID COPPER METAL BEINGDEPOSITED ON AN INERT SUPPORT, AND (4) TREATING THE ACID-TREATED,NEUTRALIZED, COPPER CONTACTED OIL WITH ADSORPTIVE CLAY.